1. Field of the Invention
The present invention relates to a semiconductor device utilizing a silicon carbide (SiC) substrate and its manufacturing method.
2. Description of the Related Art
A silicon carbide semiconductor (hereinafter, abbreviated as SiC) is capable of forming a pn junction and a forbidden band width thereof is wide as compared with other semiconductor such as a Silicon (Si) or a Gallium Arsenide (GaAs). It is reported that the forbidden band width of 3C-(C denotes a cubic system as will be described later) SiC is 2.23 eV (electron Volt), that of 6H-(H denotes a hexagonal system as will be described later) SiC is 2.93 eV, and that of 4H-SiC is 3.26 eV. As is well known, there are trade-off relationships in principle prescribed by the forbidden band width between an on resistance of a power device and a reverse direction withstanding voltage thereof and between the on resistance thereof and a switching frequency (switching speed) thereof. Hence, it is difficult to obtain a high performance exceeding a limit determined by the forbidden band of Si from currently available Si power devices. However, since, if the power device is constituted by SiC with the wide forbidden band width, the above-described trade-off relationships are largely relieved, such a power device that the on resistance, the reverse direction blocking voltage, and the switching speed have remarkably or simultaneously been improved can be realized. Furthermore, since SiC is thermally, chemically, and mechanically stable and is superior in a radiation ray withstanding characteristic, it is expected that SiC can be realized not only as a high frequency device and the power device but also as an environment withstanding characteristic semiconductor device which operates under a strict condition such as a high ambient temperature, an erosion, and radiation ray irradiation.
In a MOS (Metal Oxide Semiconductor) capacitor, SiC power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) to control a large current, and an IGBT (Insulated Gate Bipolar Transistor) to control the large current especially from among SiC devices, it is an important problem to be solved for SiC devices to be put into practice that a contact resistance on a source and a drain (n type polarity) which provides causes of a thermal loss increase and of an operating speed reduction is reduced to a negligible level and highly reliable and high performance gate insulating film and MOS interface characteristic are realized.
A technology to obtain a low contact resistance in SiC singlecrystalline has been proposed. That is to say, the following method has been proposed. After a contact metallic film is formed on SiC through a vacuum deposition, a rapid thermal annealing (RTA) is carried out for several minutes at a high temperature heat process (so-called, a contact annealing) is carried out for several minutes at a high temperature equal to or higher than 950xc2x0 C. under a vacuum or inactive gas atmosphere to form a reaction layer between SiC and the contact metal which provides a contact electrode. According to a Journal of Applied Physics, 77, page 1317 (1995) authored by J. Crofton et al., n type region of SiC substrate using an Ni (Nickel) film indicates the contact resistance of an extremely low practical level in an order of 10xe2x88x927 xcexa9cm2. According to a book authored by J. Crofton called Solid-State Electronics, 41, page 1725 (1997), p type region of SiC substrate using an Al(Aluminum)-Ti(Titanium) alloy film indicates the contact resistance of the extremely low practical level in an order of 10xe2x88x926xcexa9cm2. In addition, in recent times, the low contact resistance in an order of 10xe2x88x927xcexa9cm2 is also obtained in each of n type region and p type region of 4Hxe2x80x94SiC substrate using a thin Ni and a Tixe2x80x94Al laminated layer.
However, it has been determined that the well known RTA process described above (contact annealing) gives a harmful effect on the reliability of the gate insulating film and MOS interface characteristic if the RTA process is applied simply to the actual device. For example, a paper announced at 1999 of T. Takami at al. Extended Abstract of Symposium on Future Electron Devices 2000 (Tokyo), FED-169, page 127, (1999) has described a manufacturing method of the MOS capacitor in which, after the RTA process for one minute was carried out at 1000xc2x0 C. under the vacuum atmosphere on a thermal oxide film of about 48 nm thickness formed on an n type 4H-SiC substrate having n type epitaxial growth layer, an Al (Aluminum) electrode was formed. Then, the paper has evaluated a current-voltage characteristic (I-V characteristic) of the manufactured MOS capacitor (refer to FIGS. 1A and 1B) and a high-frequency capacitance-DC bias voltage characteristic (C-V characteristic) thereof (refer to FIG. 2). At this time, the following results were indicated as compared with a specimen to which no RTA process (without RTA) was applied. That is to say, the paper has indicated such specific data as described below and pointed out a seriousness of problem: (1) A withstanding voltage (a breakdown voltage) of the gate insulating film originally having about 40 volts was rapidly dropped to 40xc3x97xe2x85x9, viz., 5 volts or lower (refer to FIG. 1A); (2) A leakage current of the gate insulating film was remarkably increased (refer to FIG. 1A)); and (3) A flat-band voltage is shifted from an ordinary in proximity to 0 volts into a positive direction by 15 volts or higher (refer to FIG. 2). There are many reports that have pointed out in the same way. It is of course that this problem places the same importance on the power MOSFET and IGBT having the same structure as the MOS capacitor.
As a solution of the problem described above, it can easily be conceived that the temperature of the RTA process (contact annealing) is reduced to, for example, 850xc2x0 C. or lower. However, this method introduces another harmful effect such a special dislike effect on the power device as to increase the contact resistance on a source and a drain rapidly. Consequently, this method cannot be said any more a fundamental countermeasure of the above-described problem.
It is, therefore, an object of the present invention to provide a silicon carbide semiconductor device and its manufacturing method which can solve the problems of deteriorations of the gate insulating film and MOS interface characteristic caused by the RTA process during the formation of the contact on the SiC substrates without introduction of the increase in a contact resistance in an ohmic contact.
The above-described object can be achieved by providing a silicon carbide semiconductor device, comprising: a gate insulating film: an electrode member that is inactive to the gate insulating film; an insulating film that is inactive to the gate insulating film; and a singlecrystalline silicon carbide substrate, the gate insulating film being treated with a predetermined heat process after being enclosed with the electrode member, the insulating film, and the singlecrystalline silicon carbide substrate.
The above-described object can also be achieved by providing a silicon carbide semiconductor device, comprising: a gate insulating film: an electrode member that is inactive to the gate insulating film; a field insulating film that is inactive to the gate insulating film; and a singlecrystalline silicon carbide substrate, the gate insulating film being treated with a predetermined heat process after being enclosed with the electrode member, the field insulating film, and the singlecrystalline silicon carbide substrate.
The above-described object can also be achieved by providing a silicon carbide semiconductor device, comprising: comprising: a singlecrystalline silicon carbide substrate; a field insulating film formed on a surface of the substrate; a gate window opened in the field insulating film; a gate insulating film formed by a method including a thermal oxidization over the whole surface of the singlecrystalline silicon carbide substrate at the gate opening, the gate insulating film being thinner than the field insulating film; a gate electrode formed on the gate insulating film so as to cover the whole gate window; and a metal electrode that is another than the gate electrode, is contacted with the singlecrystalline silicon carbide substrate, and is treated with a predetermined heat process at a temperature which is lower than a thermal oxidization temperature by which the gate insulating film is formed and is sufficient to carry out a contact annealing between the singlecrystalline silicon carbide substrate and a metal after a whole surrounding of the gate insulating film is enclosed with the singlecrystalline silicon carbide substrate, the field insulating film, and the gate electrode.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor device, comprising: forming a field insulating film on a surface of a singlecrystalline silicon carbide substrate; forming a gate window in the field insulating film; forming a gate insulating film thinner than the field insulating film over the whole surface of the singlecrystalline silicon carbide substrate at the gate opening by a method including a thermal oxidization of at least singlecrystalline silicon carbide substrate; forming a gate electrode over the gate insulating film so as to cover the whole gate window; forming a metal electrode that is another than the gate electrode and is contacted with the singlecrystalline silicon carbide substrate; and carrying out a heating process at a temperature lower than that of the thermal oxidization by which the gate insulating film is formed and sufficient to carry out a contact annealing between the singlecrystalline silicon carbide and a metal after whole steps before this heating process have been completed.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor devices comprising: washing a surface of the singlecrystalline silicon carbide substrate having a homo-epitaxial layer; once thermally oxidizing the surface of the washed singlecrystalline silicon carbide substrate in a dry O2 ambient and, immediately thereafter, removing a sacrificial oxidization film by a hydrofluoric acid series etchant; forming a field insulating film on a washed and low-defect surface formed by the sacrificial oxidization followed by the removable of the thermal oxid; forming a predetermined gate window in the field insulating film employing a photolithography and hydrofluoric acid series etchant; cleaning the substrate surface polluted with a solution of a photoresist used in the previous step of forming the predetermined gate window with the acid treatment; forming the gate insulating film in the gate window through thermal oxidization; forming a polycrystalline silicon film to which a conductive impurity is added onto the whole surface of the substrate on which the gate insulating film is also formed; forming a gate electrode by etching the polycrystalline silicon film into a predetermined pattern by the photolithography; washing the substrate surface after removing an etching mask used in the previous step of forming the gate electrode; forming an interlayer insulating film over the whole surface of the washed substrate; evaporating an electrode material onto a rear surface of the singlecrystalline silicon carbide substrate to which a clean surface is exposed through the acid treatment and an ultra-deionized water washing; performing a contact annealing of the rear surface electrode by performing a thermal process at a temperature which is lower than that of the thermal oxidization by which the gate insulating film is formed and is sufficient to perform the contact annealing between the singlecrystalline silicon carbide and a metal; opening a gate electrode contact hole penetrated to the gate electrode at a predetermined position of the interlayer insulating film; and forming a metal interconnection on an upper part of the interlayer insulating film to which the gate electrode contact hole is opened to be connected to the gate electrode via the gate electrode contact hole, the contact annealing of the rear surface electrode being carried out after the field insulating film, the gate insulating film, and the gate electrode are formed but before the metal interconnection is formed.
The above-described object can also be achieved by providing a silicon carbide semiconductor device, comprising: a gate insulating film; a gate electrode that is inactive to the gate insulating film; an insulating film formed by thermally oxidizing a part of a member of the gate electrode; a singlecrystalline silicon carbide substrate; and another insulating film formed by thermally oxidizing the singlecrystalline silicon carbide substrate, a thermal process being carried out after the gate insulating film is enclosed with the gate electrode, the insulating film, the singlecrystalline silicon carbide substrate, and the other insulating film.
The above-described object can also be achieved by providing a silicon carbide semiconductor device comprising: a singlecrystalline silicon carbide substrate; an insulating film formed on a surface of the singlecrystalline silicon carbide by a method including a thermal oxidization; a gate electrode formed on a part of the insulating film that provides a gate insulating film; a gate electrode side wall insulating film formed by thermally oxidizing a part of a member of the gate electrode; and a metal electrode that is another than the gate electrode, is contacted with the singlecrystalline silicon carbide substrate, and is treated with a predetermined thermal process at a temperature which is lower than that of the thermal oxidization by which the gate insulating film is formed and is sufficient to carry out a contact annealing between the singlecrystalline silicon carbide substrate and a metal after a whole surrounding of the gate insulating film is enclosed with the singlecrystalline silicon carbide substrate, the field insulating film, and the gate electrode.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor device, comprising: forming an insulating film by thermally oxidizing a surface of a singlecrystalline silicon carbide substrate at a predetermined temperature; forming a gate electrode on a region of the insulating film that provides a gate insulating film; thermally oxidizing a member of the gate electrode to form a gate electrode sidewall insulating film on a sidewall of the gate electrode member; forming an interlayer insulating film on each upper surface of the gate electrode and the insulating film; evaporating a metal electrode material on a rear surface of the singlecrystalline silicon carbide substrate; and forming a rear surface electrode by carrying out a thermal process at a temperature lower than the predetermined temperature at which the surface of the singlecrystalline silicon carbide substrate is thermally oxidized and which is sufficient to perform a contact anneal between the singlecrystalline silicon carbide and a metal after a whole surrounding of the gate insulating film is enclosed by the singlecrystalline silicon carbide substrate, the insulating film formed over the singlecrystalline silicon carbide substrate, and the gate electrode side wall insulating film.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor device, comprising: forming an insulating film by thermally oxidizing a surface of a singlecrystalline silicon carbide substrate at a predetermined temperature; forming a gate electrode on a region of the insulating film that provides a gate insulating film; forming a transitory silicon nitride film on an upper surface of the gate electrode; thermally oxidizing a member of the gate electrode to form a gate electrode side wall insulating film on a side wall of the gate electrode member; eliminating the transitory silicon nitride film; forming an interlayer insulating film on upper surfaces of the gate electrode and the insulating film; evaporating a metal electrode material on a rear surface of the singlecrystalline silicon carbide substrate; and forming a rear surface electrode by carrying out a thermal process at a temperature lower than the predetermined temperature at which the surface of the singlecrystalline silicon carbide substrate is oxidized and which is sufficient to perform a contact annealing between the singlecrystalline silicon carbide and a metal after a whole surrounding of the gate insulating film is enclosed by the singlecrystalline silicon carbide substrate, the insulating film formed over the singlecrystalline silicon carbide substrate, and the gate electrode side wall insulating film.
The above-described object can be achieved by providing a silicon carbide semiconductor device comprising: a singlecrystalline silicon carbide substrate; a field insulating film formed by a method including a thermal oxidization on a surface of the singlecrystalline silicon carbide substrate; an insulating film formed on the surface of the singlecrystalline silicon carbide substrate of an window opened in the field insulating film and thermally processed during its formation or after its formation; a gate electrode formed on a part of the insulating film which provides a gate insulating film; a gate electrode side wall insulating film formed by thermally oxidizing a part of a member of the gate electrode; and a metal electrode that is another than the gate electrode, is contacted with the singlecrystalline silicon carbide substrate, and is treated with a predetermined thermal process at a temperature which is lower than a temperature of the thermal oxidization of the insulating film and is sufficient to carry out a contact annealing between the singlecrystalline silicon carbide and a metal after a whole surrounding of the gate insulating film is enclosed with the singlecrystalline silicon carbide substrate, the field insulating film, the thermally processed insulating film, the gate electrode, and the gate electrode side wall insulating film.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor device, comprising: forming a lower insulating film by thermally oxidizing a surface of a singlecrystalline silicon carbide substrate; forming an upper insulating film on an upper part of the lower insulating film; forming a window on a predetermined region of a field insulating film constituted by the lower insulating film and the upper insulating film, the window reaching to the surface of the singlecrystalline silicon carbide substrate; thermally oxidizing the surface of the singlecrystalline silicon carbide substrate in the window at a predetermined temperature to form the insulating film; forming a gate electrode above a part of the insulating film that provides a gate insulating film; thermally oxidizing a member of the gate electrode to form a gate electrode side wall insulating film on a side wall of the gate electrode member; forming an interlayer insulating film on a part of the insulating film except a lower part thereof below the gate electrode and at upper parts of the gate electrode and the upper insulating film; evaporating a metal electrode material onto a rear surface of the singlecrystalline silicon carbide substrate; and forming a rear surface electrode by performing a thermal process at a temperature which is lower than a predetermined temperature at which the insulating film is formed and is sufficient to perform a contact annealing between the singlecrystalline silicon carbide and a metal after a whole surrounding of the gate insulating film is enclosed by the singlecrystalline silicon carbide substrate, the field insulating film, the gate electrode, the gate electrode side wall insulating film, and a part of the insulating film that is other than the gate insulating film.
The above-described object can also be achieved by providing a manufacturing method for a silicon carbide semiconductor device, comprising: forming a lower insulating film by thermally oxidizing a surface of a singlecrystalline silicon carbide substrate; forming an upper insulating film on an upper part of the lower insulating film; opening a window at a predetermined region of a field insulating film constituted by the lower thermal insulating film and the upper insulating film, the window reaching to the surface of the singlecrystalline silicon carbide substrate; thermally oxidizing the surface of the singlecrystalline silicon carbide substrate at the window at a predetermined temperature to form the insulating film; forming a gate electrode above a part of the insulating film that provides a gate insulating film; forming a transitory silicon nitride film on an upper part of the gate electrode; thermally oxidizing a member of the gate electrode to form a gate electrode side wall film on a side wall of the gate electrode member; eliminating the transitory silicon nitride film; forming an interlayer insulating film on a part of the insulating film except a lower part thereof below the gate electrode and at upper parts of the gate electrode and the upper insulating film; evaporating a metal electrode material onto a rear surface of the singlecrystalline silicon carbide substrate; and forming a rear surface electrode by performing a thermal process at a temperature which is lower than a predetermined temperature at which the insulating film is formed and is sufficient to perform a contact annealing between the singlecrystalline silicon carbide and a metal after a whole surrounding of the gate insulating film is enclosed by the singlecrystalline silicon carbide substrate, the field insulating film, the gate electrode, the gate electrode side wall insulating film, and a part of the insulating film that is other than the gate insulating film.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.